In mining, after the mineral or strata is removed, providing some method of supporting the newly exposed roof is required. In mechanized mining, the majority of exposed roof is supported quickly by the application of roof bolts, mechanical devices which are inserted in holes drilled in the exposed mine roof. These roof bolts serve to tie the layers of strata together to form a self-supporting beam from the layers of roof rock. However, there is still some considerable need for the use of supplementary roof supports or “timbers”. The term “timbering” has the generic meaning of installing some direct support between the mine roof and floor regardless of the material from which it is made.
The supplementary supports have several uses and may be used to shore up and to prevent the spread of deteriorating roof strata which occurs from time to time in various places in a mine. Also, mine openings or entries (which are similar to tunnels) which are no longer used may be timbered as a preventive measure to avoid deterioration some time in the future.
However, a major use of supplementary supports is to maintain the roof in entries used as access to and around longwall mining sections or pillar extraction sections of a mine. In such locations, open entries are needed to allow air flow or access for inspection and therefore, considerable extra effort, in the form of supplemental support, is expended to maintain such entries.
Supplementary supports may be non-yielding or rigid in the form of wooden posts placed in a vertical orientation (perpendicular to the roof and floor), steel posts or stacked concrete blocks. Such non-yielding props have a distinct disadvantage in that they may fail catastrophically and with little warning when the force from the converging roof exceeds the strength of the prop. In such a situation, once the rigid support has failed, there may be less resistance remaining to prevent the roof from falling-in further. In addition, such rigid supports may tend to cause the roof and floor to deteriorate due high stresses imposed at the points of contact.
Another form of supplementary support is the yielding type. Given that the mine roof always is slowly converging (or settling), the yielding prop will give way to the roof's movement while not failing. In this manner, the prop continues to function as it is intended by providing support to the roof at a prescribed force. A well-designed yielding support could have characteristics including: a) it exerts consistent force through its operating range, b) it operates through a reasonably long effective range, c) its intended supporting force is not affected by storage or atmospheric conditions that may exist in a mine and d) it may be rapidly deployed by mine personnel.
There are numerous yielding props available including those which depend upon a friction force to develop resistance, those which depend upon a formulated cementaceous compound to crush at a prescribed force and those utilizing a regulated hydraulic pressure to yield at the prescribed force.
Many of the above mentioned products require special equipment, large crews of personnel and considerable set-up time to begin the installation process. The installed cost of such units may be quite high, a factor that cannot be overlooked in the cost-competitive mining industry.
As provided herein, the present invention presents a yielding support providing a steady and predictable support force throughout its entire range of operation and one which is easily stored and deployed for use with minimal personnel requirements.
In addition to mining applications, such supports may be utilized to support structures in other than mining situations.